It may be using conda-forge so let's try conda-forge cdt.

Author: ryanskeith

tests/test-recipes/metadata/cdt_linking/conda_build_config.yaml

@@ -1,5 +1,2 @@
 cdt_name:  # [linux]
-  - el8   # [linux]
-
-BUILD: x86_64-conda_el8-linux-gnu   # [linux and x86_64]
-BUILD: aarch64-conda_el8-linux-gnu  # [linux and aarch64]
+  - centos7   # [linux]